FIELD OF THE INVENTION
[0001] The present invention relates to improvements in the temperature dependency of the
magnetic properties of magnetic materials and permanent magnets based on Fe-B-R systems.
In the present disclosure, R denotes rare earth elements inclusive of yttrium.
BACKGROUND OF THE INVENTION
[0002] Magnetic materials and permanent magnet materials are one of the important electric
and electronic materials applied in an extensive range from various electrical appliances
for domestic use to peripheral terminal devices of large-scaled computers. In view
of recent needs for miniaturization and high efficiency of electric and electronic
equipments, there has been an increasing demand for upgrading of permanent magnet
materials and generally magnetic materials.
[0003] The permanent magnet materials developed yet include alnico, hard ferrite and samarium-cobalt
(SmCo) base materials which are well-known and used in the art. Among these, alnico
has a high residual magnetic flux density (hereinafter referred to Br) but a low coercive
force (hereinafter referred to Hc), whereas hard ferrite has high Hc but low Br.
[0004] Advance in electronics has caused high integration and miniaturization of electric
components. However, the magnetic circuits incorporated therein with alnico or hard
ferrite increase inevitably in weight and volume, compared with other components.
On the contrary, the SmCo base magnets meet a demand for miniaturization and high
efficiency of electric circuits due to their high Br and Hc. However, samarium is
rare natural resource, while cobalt should be included 50 - 60 wt % therein, and is
also distributed at limited areas so that its supply is unstable.
[0005] Thus, it is desired to develop novel permanent magnet materials free from these drawbacks.
[0006] If it could be possible to use, as the main component for the rare earth elements
use be made of light rare earth elements that occur abundantly in ores without employing
much cobalt, the rare earth magnets could be used abundantly and with less expense
in a wider range. In an effort made to cbtain such permanent magnet materials, R-Fe
2 base compounds, wherein R is at least one of rare earth metals, have been investigated.
A. E. Clark has discovered that sputtered amorphous TbFe
2 has an energy product of.29.5 MGOe at 4.2°K, and shows a coercive force Hc = 3.4
kOe and a maximum energy product (BH)max = 7 MGOe at room temperature upon heat-treated
at 300 - 500 ° C. Reportedly, similar investigations on SmFe
2 indicated that 9.2 MGOe was reached at 77°K. However, these materials are all obtained
by sputtering in the form of thin films that cannot be generally used as magnets,
e.g., speakers or motors. It has further been reported that melt-quenched ribbons
of PrFe base alloys show a coercive force He of as high as 2.8 kOe.
[0007] In addition, Koon et al discovered that, with melt-quenched amorphous ribbons of
(Fe
0.82B
0.18)
0.9Tb
0.05La
0.05' Hc of 9 kOe was reached upon annealed at 627°C (Br=
5kG). However, (BH)max is then low due to the unsatisfactory loop squareness of magnetization
curves (N. C. Koon et al, Appl. Phys. Lett. 39 (10), 1981, pp. 840 - 842).
[0008] Moreover, L. Kabacoff et al reported that among melt-quenched ribbons of (Fe
0.8B
0.2)
1-xPr
x (x=0-0.03 atomic ratio), certain ones of the Fe-Pr binary system show He on the kilo
oersted order at room temperature.
[0009] These melt-quenched ribbons or sputtered thin films are not any practical permanent
magnets (bodies) that can be used as such. It would be practically impossible to obtain
practical permanent magnets from these ribbons or thin films.
[0010] That is to say, no bulk permanent magnet bodies of any desired shape and size are
obtainable from the conventional Fe-B-R base melt-quenched ribbons or R-Fe base sputtered
thin films. Due to the unsatisfactory loop squareness (or rectangularity) of the demagnetization
curves, the Fe-B-R base ribbons heretofore reported are not taken as the practical
permanent magnet materials comparable with the conventional, ordinary magnets. Since
both the sputtered thin films and the melt-quenched ribbons are magnetically isotropic
by nature, it is indeed almost impossible to obtain therefrom magnetically anisotropic
(hereinbelow referred to "anisotropic") permanent magnets for the practical purpose
comparable to the conventional hard ferrite or SmCo magnets.
SUMMARY OF THE DISCLOSURE
[0011] An essential object of the present invention is to provide novel magnetic materials
and permanent magnets based on the fundamental composition of Fe-B-R having an improved
temperature dependency of tha magnetic properties.
[0012] Another object of the present invention is to provide novel practical'permanent magnets
and magnetic materials which do not share any disadvantages of the prior art magnetic
materials hereinabove mentioned.
[0013] A further object of the present invention is to provide novel magnetic materials
and permanent magnets having good temperature dependency and magnetic properties at
room or elevated temperatures.
[0014] A still further object of the present invention is to provide novel magnetic materials
and permanent magnets which can be formed into any desired shape and practical size.
[0015] A still further object of the present invention is to provide novel permanent magnets
having magnetic anisotropy and excelling in both magnetic properties and mechanical
strength.
[0016] A still further object of the present invention is to provide novel magnetic materials
and permanent magnets in which as R use can effectively be made of rare earth element
occurring abundantly in nature.
[0017] Other objects of the present invention will become apparent from the entire disclosure
given herein.
[0018] The magnetic materials and permanent magnets according to the present invention are
essentially formed of alloys comprising novel intermetallic compounds, and are crystalline,
said intermetallic compounds being characterized at least by new Curie points Tc.
[0019] In the followings the term "percent" or "%" denotes the atomic percent (abridged
as "at %") if not otherwise specified.
[0020] According to the first aspect of the present invention, there is provided a magnetic
material comprising Fe, B, R (at least one of the rare earth elements including Y)
and Co, and having its major phase formed of Fe-Co-B-R type compound that is of the
substantially tetragonal system crystal structure.
[0021] According to the second aspect of the present invention, there is provided a sintered
magnetic material having its major phase formed of a compound consisting essentially
of, in atomic ratio, 8 to 30 % of R (wherein R represents at least one of the rare
earth elements including Y), 2 to 28 % of B, no more than 50 % of Co (except that
the amount of Co is zero) and the balance being Fe and impurities.
[0022] According to the third aspect of the present invention, there is provided a sintered
magnetic material having a composition similar to that of the aforesaid sintered magnetic
material, wherein the major phase is formed of an Fe-Co-B-R type compound that is
of the substantially tetragonal system.
[0023] According to the fourth aspect of the present invention; there is provided a sintered
permanent magnet (an Fe-Co-B-R base permanent magnet) consisting essentially of, in
atomic ratio, 8 to 30 % of R (at least one of the rare earth elements including Y)
, 2 to 28 % of B, no more than 50 % of Co (except that the amount of Co is zero) and
the balance being Fe and impurities. This magnet is anisotropic.
[0024] According to the fifth aspect of the present invention, there is provided a sintered
anisotropic permanent magnet having a composition similar to that of the fourth permanent
magnet, wherein the major phase is formed by an Fe-Co-B-R type compound that is of
the substantially tetragonal system crystal structure.
[0025] Fe-Co-B-R base magnetic materials according to the 6th to 8th aspects of the present
invention are obtained by adding to the first - third magnetic materials the following
additional elements M, provided, however, that the additional elements M shall individually
be added in amounts less than the values as specified below, and that, when two or
more elements M are added, the total amount thereof shall be less than the upper limit
of the element that is the largest, among the elements actually added (For instance,
Ti, V and Nb are added, the sum of these must be no more than 12.5 % in all.):

[0026] F-e-B-R-Co base permanent magnets according to the 9th to and 10th aspects of the
present invention are obtained by adding respectively to the 4th and 5th permanent
magnets the aforesaid additional elements M on the same condition.
[0027] Due to the inclusion of Co, the invented magnetic materials and permanent magnets
have a Curie point higher than that of the Fe-B-R type system or the Fe-B-R-M type
system.
[0028] With the permanent magnets of the present invention, practically useful magnetic
properties are obtained if the mean crystal grain size of the intermetallic compound
is in a range of about 1 to about 100 µm for both the Fe-Co-B-R and Fe-Co-B-R-M systems.
[0029] Furthermore, the inventive permanent magnets can exhibit good magnetic properties
by containing 1 vol. % or higher of nonmagnetic intermetallic compound phases.
[0030] The inventive magnetic materials are advantageous in that they can be obtained in
the form of at least as-cast alloys, or powdery or granular alloys or sintered bodies
in any desired shapes, and applied to magnetic recording media (such as magnetic recording
tapes) as well as magnetic paints, magnetostrictive materials, thermosensitive materials
and the like. Besides, the magnetic materials are useful as the intermediaries for
the production of permanent magnets.
[0031] The magnetic materials and permanent magnets according to the present invention are
superior in. mechanical strength and machinability to the prior art alnico, R-Co type
magnets, ferrite, etc., and has high resistance against chipping-off on machining.
[0032] In the following the present invention will be elucidated with reference to the accompanying
Drawings which, however, are being presented for illustrative purpose.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033]
Fig. 1 is a graph showing relationship between the Curie point and the amount of Co
of one embodiment of the present invention, with the atomic percent of Co as abscissa;
Fig. 2 is a graph showing the relationship between the amount of B and Br as well
as iHc (kOe) of one embodiment of Fe-10Co-xB-15Nd, with the atomic percent of B as
abscissa;
Fig. 3 is a graph showing the relationship between the amount of Nd and Br (kG) as
well as iHc (kOe) of one embodiment of Fe-lOCo-8B-xNd, with the atomic percent of
Nd as abscissa;
Fig. 4 is a view showing the demagnetization curves of one embodiment of the present
invention (1 is the initial magnetization curve 2 the demagnetization curve), with
4πI (kG) as ordinate and a magnetic field H (kOe) as abscissa;
Fig. 5 is a graph showing the relationship between the amount of Co (abscissa) and
the Curie point of one embodiment of the present invention;
Fig. 6 is a graph showing the demagnetization curves of one embodiment of the present
invention, with a magnetic field H (kOe) as abscissa and 4πI (kG) as ordinate;
Figs. 7 to 9 are graphs showing the relationship between the amount of additional
elements M and the residual magnetization Br (kG);
Fig. 10 is a graph showing the relationship between iHc and the mean crystal grain
size D (log-scale abscissa in µm) of one embodiment of the present invention;
Fig. 11 is a graph showing the demagnetization curves of one embodiment of the present
invention;
Fig. 12 is a Fe-B-R ternary system diagram showing compositional ranges corresponding
to the maximum energy products (BH)max (MGOe) for one embodiment of an Fe-5Co-B-R
system;
Fig. 13 is a graph showing the relationship between the amount of Cu, C, P and S (abscissa)
and Br of one embodiment of the present invention;
Fig. 14 is an X-ray diffraction pattern of one embodiment of the invention and
Fig. 15 is a flow chart of the experimental procedures of powder X-ray analysis and
demagnetization curve measurements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] The present inventors have found magnetic materials and permanent magnets of the
Fe-B-R system the magnets comprised of magnetically anisotropic sintered bodies to
be new high-performance permanent magnets without employing expensive Sm and Co, and
disclosed them in a European patent application filed on July 5, 1983 No.83106573.5
based on a Japanese Patent Application No. 57-145072. The Fe-B-R base permanent magnets
contain Fe as the main component and light-rare earth elements as R,' primarily Nd
and Pr, which occur abundantly in nature, and contain no Co. Nonetheless, they are
excellent in that they can show an energy product reaching as high as 25 - 35 MGOe
or higher. The Fe-B-R base permanent magnets possess high characteristics at costs
lower than required in the case with the conventional alnico and rare earth-cobalt
alloys. That is to say, they offer higher cost-performance and, hence, greater advantages
as they stand.
[0035] As disclosed in the above Application, the Fe-B-R base permanent magnets have a Curie
point of generally about 300°'C and at most 370°C. The entire disclosure of said Application
is herewith incorporated herein with reference thereto with respect to the Fe-B-R
type magnets and magnetic materials. Such a Curie point is considerably low, compared
with the Curie points amounting to about 800°C of the prior art alnico or R-Co base
permanent magnets. Thus, the Fe-B-R base permanent magnets have their magnetic properties
more dependent upon temperature, as compared with the alnico or R-Co base magnets,
and are prone to deteriorate magnetically when used at elevated temperatures.
[0036] As mentioned above, the present invention has for its principal object to improve
the temperature dependency of the magnetic properties of the Fe-B-R base magnets and
generally magnetic materials. According to the present invention, this object is achieved
by substituting part of Fe, a main component of the Fe-B-R base magnets, with Co so
as to increase the Curie point of the resulting alloy. The results of researches have
revealed that the Fe-B-R base .magnets are suitably used in a usual range of not higher
than 70°C, since the magnetic properties deteriorate at temperature higher than about
100°C. As a result of various experiments and studies, it has thus been found that
the substitution of Co for Fe is effective for improving the resistance to the temperature
dependency of the Fe-B-R base permanent magnets and magnetic materials.
[0037] More specifically, the present invention provides permanent magnets comprised of
anisotropic sintered bodies consisting essentially of, in atomic percent, 8 to 30
% R (representing at least one of the :aare earth elements including yttrium), 2 to
28 % of B and the balance being Fe and inevitable impurities, in which part of Fe
is substituted with Co to incorporate 50 at % or less of Co in the alloy compositions,
whereby the temperature dependency of said permanent magnets are substantially increased
to an extent comparable to those of the prior art alnico and R-Co base alloys.
[0038] According to the present invention, the presence of Co does not only improve the
temperature dependency of the Fe-B-R base permanent magnets, but also offer additional
advantages. That is to say, it is possible to attain high magnetic properties through
the use of light-rare. earth elements such as Nd and Pr which occur abundantly in
nature. Thus, the present Co-substituted Fe-B-R base magnets are superior to the existing
R-Co base magnets from the standpoints of both natural resource and cost as well as
magnetic properties.
[0039] It has further been revealed from extensive experiments that the resistance to the
temperature dependency and the magnetic properties best-suited for permanent magnets
are attained in the case where part of Fe is replaced by Co, the crystal structure
is substantially of the tetragonal system, and the mean crystal grain size of the
sintered body having a substantially tetragonal system crystal structure is in a certain
range. Thus, the present invention makes it possible to ensure industrial production
of high-performance sintered permanent magnets based on the Fe-Co-B-R system in a
stable manner.
[0040] By measurements, it has been found that the Fe-Co-B-R base alloys have a high crystal
magnetic anisotropy constant Ku and an anisotropic magnetic field Ha standing comparison
with that of the existing Sm-Co base magnets.
[0041] According to the theory of the single domain particles, magnetic substances having
high anisotropy field
Ha potentially provide fine particle type magnets with high-performance as is the case
with the hard ferrite or SmCo base magnets. From such a viewpoint, sintered, fine
particle type magnets were prepared with wide ranges of composition and varied crystal
grain size after sintering to determine the permanent magnet properties thereof.
[0042] As a consequence, it has been found that the obtained magnet properties. correlate
closely with the mean crystal grain size after sintering. In general, the single magnetic
domain, fine particle type magnets magnetic walls which are formed within each particles,
if the particles are large. For this reason, inversion of magnetization easily takes
place due to shifting of the magnetic walls, resulting in a low Hc. On the contrary,
if the particles are reduced in size to below a certain value, no magnetic walls are
formed within the particles. For this reason, the inversion of magnetization proceeds
only by rotation, resulting in high Hc. The critical size defining the single magnetic
domain varies depending upon diverse materials, and has been thought to be about 0.01
um for iron, about 1 µm for hard ferrite, and about 4 µm for SmCo.
[0043] The He of various materials increases around their critical size. In the Fe-Co-B-R
base permanent magnets of the present invention, Hc of 1 kOe or higher is obtained
when the mean crystal grain size ranges from 1 to 100 µm, while He of 4 kOe or higher
is obtained in a range of 1.5 to 50 µm.
[0044] The permanent magnets according to the present invention are obtained as sintered
bodies. Thus, the crystal grain size of the sintered body after sintering is of the
primary concern. It has experimentally been ascertained that, in order to allow the
He of the sintered compact to exceed 1 kOe, the mean crystal grain size should be
no less than about 1 µm after sintering. In order to obtain sintered bodies having
a smaller crystal grain size than this, still finer powders should be prepared prior
to sintering. However, it is then believed that the He of the sintered bodies decrease
considerably, since the fine powders of the Fe-Co-B-R alloys are susceptible to oxidation,
the influence of distortion applied upon the fine particles increases, superparamagnetic
substances rather than ferromagnetic substances are obtained when the grain size is
excessively reduced, or the like. When the crystal grain size exceeds 100 pm, the
obtained particles are not single magnetic domain particles, and include magnetic
walls therein, so that the inversion of magnetization easily takes place, thus leading
to a drop in Hc. A grain size of no more than 100 µm is required to obtain Hc of no
less than 1 kOe. Particular preference is given to a range of 1.5 to 50 µm, within
which Hc of 4 kOe or higher is attained.
[0045] It should be noted that the Fe-Co-B-R-M base alloys to be discussed later also exhibit
the magnetic properties useful for permanent magnets, when the mean crystal grain
size is between about 1 and about 100 µm, preferably 1.5 and 50 µm.
[0046] It is generally observed that, as the amount of Co incorporated in Fe-alloys increases,
some Fe alloys increase in Curie point (Tc), while another decrease in that point.
For this reason, the substitution of Fe with Co generally causes complicated results
which are almost unexpectable. As an example, reference is made to the substitution
of Fe in RFe
3 compounds with Co. As the amount of Co increases, Tc first increases and peakes substantially
at a point where a half of Fe is replaced by Co, say, R(Fe
0.5Co
0.5)
3 is obtained, and thereafter decreases. In the case of Fe
2B alloys, Tc decreases with certain gradient by the substitution of Fe with Co.
[0047] According to the present invention, it has been noted that, as illustrated in Fig.
1, Tc increases with increases in the amount of Co, when Fe of the Fe-B-R system is
substituted with Co. Parallel tendencies have been observed in all the Fe-B-R type
alloys regardless of the type of R. Even a slight amount of Co is effective for the
increase in Tc and, as will be seen from a (77-x)Fe-xCo-8B-15Nd alloy shown by way
of example in Fig. 1, it is possible to obtain alloys having any desired Tc between
about 310 and about 750°C by regulation of x. In the Co-substituted Fe-B-R base permanent
magnets according to the present invention, the total composition of B, R and (Fe
plus Co) is essentially identical with that of the Fe-B-R base alloys (without Co).
[0048] Boron (B) shall be used on the one hand in an amount no less than 2 % so as to meet
a coercive force of 1 kOe or higher and, on the other hand, in an amount of not higher
than 28 % so as to exceed the residual magnetic flux density Br of about 4 kG of hard
ferrite. R shall be used on the one hand in an amount no less than 8 % so as to obtain
a coercive force of 1 kOe or higher and, on the other hand, in an amount of 30 % or
less since it is easy to burn, incurs difficulties in handling and preparation, and
is expensive.
[0049] The present invention offers an advantage in that less expensive light-rare earth
element occurring abundantly in nature can be used as R since Sm is not necessarily
requisite nor necessarily requisite as a main component.
[0050] The rare earth elements used in the magnetic materials and the permanent magnets
according to the present invention include light- and heavy-rare earth elements inclusive
of Y, and may be applied alone or in combination. Namely, R includes Nd, Pr, La, Ce,
Tb, Dy, Ho, Er, Eu, Sm, Gd, Pm, Tm, Yb, Lu and Y. Preferably, the light rare earth
elements amount to no less than 50 at % of the overall rare earth elements R, and
particular preference is given to Nd and Pr. More preferably Nd plus Pr amounts to
no less than 50 at % of the overall R. Usually, the use of one rare earth element
will suffice, but, practically, mixtures of two or more rare earth elements such as
mischmetal, didymium, etc. may be used due to their ease in avilability. Sm, Y, La,
Ce, Gd and the like may be used in combination with other rare earth elements such
as Nd, Pr, etc. These rare earth elements R are not always pure rare earth elements
and, hence, may contain impurities which are inevitably entrained in the production
process, as long as they are technically available.
[0051] Boron represented by B may be pure boron or ferroboron, and those containing as impurities
Al, Si, C etc. may be used.
[0052] Having a composition of 8 - 30 at % R, 2 - 28 at % B, 50 at % or less Co, and the
balance Fe with the substantially tetragonal system crystal structure after sintering
and a mean crystal grain size of 1 - 100 µm, the permanent magnets according to the
present invention have magnetic properties such as coercive force He of Z 1 kOe, and
residual magnetic flux density Br of > 4 kG, and provide a maximum energy product
(BH)max value which is at least equivalent or superior to the hard ferrite (on the
order of up to 4 MGOe). Due to the presence of Co in an amount of 5 % or more the
thermal coefficient of Br is about 0.1 %/°C or less. If R ranges from 12 to 24 %,
and B from 3 to 27 %, (BH) max ≥ about 7 MGOe is obtainable so far as R and B concern.
[0053] When the light rare earth elements are mainly used as R (i.e., those elements amount
to 50 at % or higher of the overall R) and a composition is applied of 12 - 24 at
% R, 4 - 24 at % B, 5 - 45 at % Co, with the balance being Fe, maximum energy product
(BH)max of ≥ 10 M
GOe and said thermal coefficient of Br as above are attained. These ranges are more
preferable, and (BH)max reaches 33 MGOe or higher.
[0054] Referring to the Fe-5Co-B-R system for instance, the ranges surrounded with contour
lines of (BH)max 10, 20, 30 and 33 MGOe in Fig. 12 define the respective energy products.
The Fe-20Co-B-R system can provide substantially the same results.
[0055] Compared with the Fe-B-R ternary magnets, the Co-containing Fe-B-R base magnets of
the present invention have better resistance against the temperature dependency, substantially
equivalent Br, equivalent or slightly less iHc, and equivalent or higher (BH)max since
the loop squareness or rectangularity is improved due to the presence of Co.
[0056] Since Co has a corrosion resistance higher than Fe, it is possible to afford corrosion
resistance to the Fe-B-R base magnets by incorporation of Co. Particularly Oxidation
resistance will simplify the handling the powdery materials and for the final powdery
products.
[0057] As stated in the foregoing, the present invention provides embodiments of magnetic
materials and permanent magnets which comprise 8 to 30 at % R (R representing at least
one of rare earth element including yttrium), 2 to 28 at % B, 50 at % or less Co (except
that the amount of Co is zero), and the balance being Fe and impurities which are
inevitably entrained in the process of production (referred to "Fe-Co-B-R type".
[0058] The present invention provides further embodiments which contain one or more additional
elements M selected from the group given below in the amounts of no more than the
values specified below wherein when two or more elements of M are contained, the sum
of M is no more than the maximum value among the values specified below of said elements
M actually added and the amount of M is more than zero:

[0059] The incorporation of the additional elements M enhances Hc resulting in an improved
loop squareness.
[0060] The allowable limits of typical impurities contained in the final or finished products
of magnetic materials or magnets are up to 3.5, preferably 2.3, at % for Cu; up to
2.5, preferably 1.5, at % for S; up to 4.0, preferably 3.0, at % for C; up to 3.5,
preferably 2.0, at % for P; and at most 1 at % for O (oxygen), with the proviso that
the total amount thereof is up to 4.0, preferably 3.0, at %. Above the upper limits,
no energy product of 4 MGOe is obtained, so that such magnets as contemplated in the
present invention are not obtained (see Fig. 11). With respect to Ca, Mg and Si, they
are allowed to exist each in an amount up to about 8 at %, preferably with the proviso
that their total amount shall not exceed about 8 at %. It is noted that, although
Si has effect" upon increases in Curie point, its amount is preferably about 8 at
% or less, since iHc decreases sharply in an amount exceeding 5 at %. In some cases,
Ca and Mg may abundantly be contained in R raw materials such as commercially available
Neodymium or the like.
[0061] Iron as a starting material for instance includes following impurities (by wt %)
not exceeding the values below: 0.03 C, 0.6 Si, 0.6 Mn, 0.5 P, 0.02 S, 0.07 Cr, 0.05
Ni, 0.06 Cu, 0.05 Al, 0.05 0
2 and 0.003 N
2.
[0062] Electrolytic iron generally with impurities as above mentioned of 0.005 wt % or less
is available.
[0063] Impurities included in starting ferroboron (19 - 13 % B) alloys-are not exceeding
the values below, by wt %: 0.1 C, 2.0 Si, 10.0 Al, etc.
[0064] Starting neodymium material includes impurities, e.g., other rare earth element such
as La, Ce, Pr and Sm; Ca, Mg, Ti, Al, 0, C or the like; and further Fe, Cl, F or Mn
depending upon the refining process.
[0065] The permanent magnets according to the present invention are prepared by a so-called
powder metallurgical process, i.e., sintering, and can be formed into any desired
shape and size, as already mentioned. However, desired practical permanent magnets
(bodies) were not obtained by such a melt-quenching process as applied in the preparation
of amorphous thin film alloys, resulting in no practical coercive force at all.
[0066] On the other hand, no desired magnetic properties (particularly coercive force) were
again obtained at all by melting, casting and aging used in the production of alnico
magnets, etc.. The reason is presumed to be that crystals having a coarser grain size
and a ununiform composition are obtained. Other various techniques have been attempted,
but none have given any results as contemplated.
[0067] In accordance with the present invention, however, practical permanent magnets (bodies)
of any desired shape are obtained by forming and sintering powder alloys, which magnets
have the end good magnetic properties and mechanical strength. For instance, the powder
alloys are obtainable by melting, casting and grinding or pulverization.
[0068] The sintered bodies can be used in the as-sintered state as useful permanent magnets,
and may of course be subjected to aging as is the case in the conventional magnets.
[0069] The foregoing discussions also held for both the Fe-Co-B-R system and the Fe-Co-B-R-M
system.
PREPARATION OF MAGNETIC MATERIALS
[0070] Typically, the magnetic materials of the present invention may be prepared by the
process forming the previous stage of the overall process for the preparation of the
permanent magnets of the present invention. For example, various elemental metals
are melted and cast into alloys having a tetragonal system crystal structure, which
are then finely ground into fine powders.
[0071] As the magnetic material use may be made of the powdery rare earth oxide R
20
3 (a raw material for R). This may be heated with powdery Fe, powdery Co, powdery FeB
and a reducing agent (Ca, etc) for direct reduction. The resultant powder alloys show
a tetragonal system as well.
[0072] The powder alloys can further be sintered into magnetic materials. This is true for
both the Fe-Co-B-R base'and the Fe-Co-B-R-M base magnetic materials.
[0073] The Fe-Co-B-R base magnets of the present invention will now be explained with reference
to the examples, which are given for the purpose of illustration alone, and are not
intended to limit the invention.
[0074] Fig. 1 typically illustrates changes in Curie point Tc of 77Fe-8B-15Nd wherein part
of Fe is substituted with Co(x), and (77-x)Fe-xCo-8B-15Nd wherein x varies from 0
to 77. The samples were prepared in the following steps.
[0075] (1) Alloys were melted by high-frequency melting and cast in a water-cooled copper
mold. As the starting materials for Fe, B and R use was made of, by weight ratio for
the purity, 99.9 % electrolytic iron, ferroboron alloys of 19.38 % B, 5.32 % Al, 0.74
% Si, 0.03 % C and the balance Fe, and a rare earth element or elements having a purity
of 99.7 % or higher with the impurities being mainly other rare earth elements, respectively.
As Co, electrolytic Co having a purity of 99.9 % was used.
[0076] (2) Pulverization : The castings were coarsely ground in a stamp mill until they
pass through a 35-mesh sieve, and then finely pulverized in a ball mill for 3 hours
to 3 - 10 µm.
[0077] (3) The resultant powders were oriented in a magnetic field of 10 kOe and compacted
under a pressureof 1.5 t/cm
2.
[0078] (4) The resultant compacts were sintered at 1000 - 1200 °C for about one hour in
an argon atmosphere and, thereafter, allowed to cool.
[0079] Blocks weighing about 0.1 g were obtained from the sintered bodies by cutting, and
measured on their Curie points using a vibrating sample magnetometer in the following
manner. A magnetic field of 10 kOe was applied to the samples, and changes in 4πI
depending upon temperature were determined in a temperature range of from 250°C to
800°C. A temperature at which 4πI reduced virtually to zero was taken as Curie point
Tc.
[0080] In the above-mentioned systems, Tc increased rapidly with the increase in the amount
of
Co replaced for Fe, and exceeded 600°C in Co amounts of no less than 30 %.
[0081] In the permanent magnets, increases in Tc are generally considered to be the most
important factor for reducing the changes in the magnetic properties depending upon
temperature. To ascertain this point, a number of permanent magnet samples as tabulated
in Table 1 were prepared according to the procedures as applied for the preparation
of those used in Tc measurements to determine the temperature dependency of Br.
[0082] (5) The changes in Br depending upon temperature were measured in the following manner.
Magnetization curves are obtained at 25°C, 60°C and 100°C, respectively, using a BH
tracer, and the changes in Br at between 25 and 60°C and between 60 and 100°C were
averaged. Table 1 shows the thermal coefficient of Br and the measurement results
of magnetization curves at 25°C, which were obtained of various Fe-B-R and Fe-Co-B-R
base magnets.
[0083] From Table 1, it is evident that the changes in Br depending upon temperature are
reduced by incorporation of Co into the Fe-B-R base magnets. Namely, thermal coefficients
of about 0.1 %/°C or less are obtained if Co is 5 % or more.
[0084] Table 1 also shows the magnetic properties of the respective samples at room temperature.
[0085] In most of the compositions, iHc generally decreases due to the Co substitution,
but (BH)max increases due to the improved loop rectangularity of the magnetization
curves. However, iHc decreases if the amount of Co increases from 25 to 50 7% finally
reaching about the order of 1.5 kOe. Therefore the amount of Co shall be no higher
than 50 % so as to obtain iHc Z 1 kOe suitable for permanent magnets.
[0086] From Table 1 and Fig. 1 the relationship between the Co amount and the magnetic properties
is apparent. Namely, even a small amount of Co is correspondingly effective for the
improvement of Tc. In a range of 25 % or less Co, other magnetic properties (particularly,
the energy product) are substantially not affected. (See, samples
*2, and 8 - 12 of Table 1). If Co exceeds 25 %, (BH)max also decreases.
[0087] The reasons already given in connection with the upper and lower limits of B and
the lower limit of R will be confirmed from Table 1, Fig. 2 and Fig. 3.

[0088] As a typical embodiment of the sintered magnetic magnets of the Fe-Co-B-R system
in which part of Fe is substituted with Co, Fig. 2 shows an initial magnetization
curve 1 for 57Fe-20Co-8B-15Nd at room temperature.
[0089] The initial magnetizaton curve 1 rises steeply in a low magnetic field, and reaches
saturation. The demagnetization curve 2 shows very high loop rectangularity, which
indicates that the magnet is a typical high-performance anisotropic magnet. From the
form of the initial magnetization curve 1, it is thought that this magnet is a so-called
nucleation type permanent magnet since the SmCo type magnets of the nucleation type
shows an analogous curve, wherein the coercive force of which is determined by nucleation
occurring in the inverted magnetic domain. The high loop rectangularity of the demagnetization
curve 2 indicates that this mgnet is a typical high-performance anisotropic magnet.
Other samples according to the present invention set forth in Table 1 all showed magnetization
curves similar to that of Fig. 4.
[0090] A number of magnets using primarily as R light-rare earth element such as Nd, Pr,
etc., are shown in Table 1, from which it is noted that they possess high magnetic
properties, and have their temperature dependency further improved by the substitution
of Fe with Co. It is also noted that the use of
'a mixture of two or more rare earth element as R is also useful.
[0091] Permanent magnet samples of Fe-Co-B-R-M alloys containing as M one or two additional
elements were prepared in a manner similar to that applied for the preparation of
the Fe-Co-B-R base magnets.
[0092] The additional elements M used were Ti, Mo, Bi, Mn, Sb, Ni, Sn, Ge and Ta each having
a purity of 99 %, by weight so far as the purity concerns as hereinbelow, W having
a purity of 98 %, Al having a purity of 99.9 %, and Hf having a purity of 95 %. As
V ferrovanadium containing 81.2 % of V; as Nb ferroniobium containing 67.6 % of Nb;
as Cr ferrochromium - containing 61.9 % of Cr; and as Zr ferrozirconium containing
75.5 % of Zr were used, respectively.
[0093] A close examination of the samples having a variety of compositions was carried out
by the determination of iHc, Br, (BH)max, etc. As a result, it has been found that,
in quintinary or multicomponent systems based on Fe-Co-B-R-M (wherein M represents
one or two or more additional elements), there is a certain region in which high permanent
magnet properties are developed.
[0094] Table 2 shows the maximum energy product (BH)max, which is the most important factor
of the permanent magnet properties, of typical samples. In Table 2, Fe is the balance.
[0095] From Table 2, it has been appreciated that the Fe-Co-B-R-M base magnets have high
energy product of 10 MGOe or greater over a wide compositional range.
[0096] This table mainly enumerates the examples of alloys containing Nd and Pr, but any
of 15 rare earth element (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)
give rise. to increase in (BH)max. However, the alloys containing Nd and Pr according
to the present invention are more favorable than those containing as the main materials
other rarer rare earth element (Sm, Y and heavy-rare element), partly because Nd and
Pr occur relatively abundantly in rare earth ores, and especially because no applications
of Nd in larger amounts have been found.
[0097] Also in the Fe-Co-B-R-M alloys, Co has no noticeable influence upon (BH)max, when
it is added in an amount of 25 % or less and Co contributes to the increase in the
Curie points with the increasing Co amount as is the case for the Fe-Co-B-R alloys.
For instance, comparisons of Sample Nos. 48 with 50, 58 with 60, and 68 with 70 reveal
that a compositional difference in the amount of Co (1 to 10 Co) between these alloys
causes no noticeable difference in (BH)max. Fig. 5 shows the relationship between
the Curie point and the amount of Co (by at %) of the Fe-Co-B-R-M alloys wherein M
is V, Nb, Zr and Cr, and indicates that the Curie point increases with increases in
the amount of Co, but the addition of M gives rise to substantially no remarkable
change in the Curie point.
[0098] Parallel tendencies have been observed in the Fe-Co-B-R-M fundamental alloys regardless
of the type of R. Even a slight amount of Co, e.g., 1 % is effective for Tc increases,
and it is possible to obtain alloys having any desired Tc between about 310°C and
about 750
*C by varying of x, as will be evident from the (76 - x) Fe-xCo-8B-15Nd-lM system exemplified
in Fig. 5.
[0099] Accordingly, it has turned out that with respect to the Fe-Co-B-R-M system the relationships
between the Co amount and the magnetic properties, and between the ranges of B and
R and the magnetic properties are established analogously to the Fe-Co-B-R system
previously discussed, provided that the effect of the additional elements M acts additionally.
[0100] The Fe-Co-B-R-M magnets according to the present invention have Curie points higher
than the Fe-B-R-M magnets without Co.
[0101] In the Fe-Co-B-R-M magnets, most of M have an effect upon increases in Hc. Fig. 6
shows the demagnetization curves of the typical examples of the Fe-Co-B-R-M magnets
and M-free Fe-Co-B-R magnets given for the purpose of comparison. In this figure,
reference numerals 1 to 3 denote the demagnetization curves of a M-free magnet, a
Nb-containing magnet (Table 1 No.3) and a W-containing magnet (Table 1 No. 83), respectively.
[0102] An increase in He due to the addition of M provides an increased stability and wide
applicability of the permanent magnets. However, the greater the amount of M, the
lower the Br and (BH)max will be, due to the fact that they are nonmagnetic materials
(except Ni). Since permanent magnets having slightly reduced (BH)max but high Hc have
recently been often required in certain fields, the addition of M is very useful,
however, provided that (BH)max is at least 4 MGOe.
[0103] To ascertain the effect of M upon Br, Br was measured in varied amounts of M. The
results are summarized in Figs. 7 to 9. As. seen from Figs. 7 to 9, the upper limits
of the additional elements M (Ti, Zr, Hf, V, Ta, Nb, Cr, W, Mo, Sb, Sn, Ge and Al)
other than Bi, Ni, and Mn may be chosen such that Br is at least equivalent to about
4 kG of hard ferrite. A preferable range in view of Br should be appreciated from
Figs. 7 to 9 by defining the Br range into 6.5 kG, 8kG, 10 kG or the like stages.
[0104] Based on these figures, the upper limits of the amounts of additional elements M
are fixed at the following values at or below which (BH)max is at least equivalent
or superior to about 4 MGOe of hard ferrite:

[0105] When two or more elements M are employed, the resulting characteristic curve will
be depicted between the characteristic curves of the individual elements in Fig. 7
to 9. Thus each amount of the individual elements M are within each aforesaid range,
and the total amount thereof is no more than the maximum values among the values specified
for the individual elements which are actually added and present in a system. For
instance, if Ti, V and Nb are added the total amount of these must be mo more than
12.5% in all.
[0106] A more preferable range for the amount of M is determined from a range of (BH)max
within which it exceeds 10 MGOe of the highest grade alnico. In order that (BH)max
is no less than 10 MGOe, Br of 6.5 kG or higher is required.
[0107] From Figs. 7 to 9, the upper limits of the amounts of M are preferably defined at
the following values:

wherein two or more additional elements M are used, the preferable ranges for M are
obtained when the individual elements are no higher than the aforesaid upper limits,
and the total amount thereof is,no higher than the maximum values among the values
allowed for the individual pertinent elements which are actually added and present.
[0108] Within the upper limits of M, when the Fe-Co-B-R base system preferably comprises
4 to 24 % of B, 11 to 24 % of R (light-rare earth elements, primarily Nd and Pr),
and the balance being the given amounts of" Fe and Co, (BH)max of 10 MGOe or higher
is obtained within the preferable ranges of the additional elements M, and reaches
or exceeds the (BH)max level of hard ferrite within the upper limit of M.
[0109] Even when the Fe-Co-B-R base system departs from the above-mentioned preferable range,
(BH)max exceeding that of hard ferrite is obtained, if the additional element M are
in" the above-mentioned preferable range. According to more preferable embodiments
of the present invention, the permanent magnets have (BH)max of 15, 20, 25, 30 and
even 33 MGOe or higher.
[0110] In general, the more the amount of M, the lower the Br; however, most elements of
M serve to increase iHc. Thus, (BH)max assumes a value practically similar to that
obtained with the case where no M is applied, through the addition of an appropriate
amount of M, and may reach at most 33 MGOe or higher. The increase in coercive force
serves to stabilize the magnetic properties, so that permanent magnets are obtained
which are practically very stable and have a high energy product.
[0111] If large amounts of Mn and Ni are incorporated, iHc will decrease; there is only
slilght decrease in Br due to the fact that Ni is a ferromagnetic element (see Fig.
8). Therefore, the upper limit of Ni is 8 %, preferably 6.5 %, in view of Hc.
[0112] The effect of Mn upon decrease in Br is not strong but larger than is the case with
Ni. Thus, the upper limit of Mn is 8 %, preferably 6 %, in view of iHc.
[0114] The relationship between the crystal grain size and the magnetic properties of the
Fe-Co-B-R base magnets will be described in detail hereinbelow.
[0115] The pulverization procedure as previously mentioned was carried out for varied periods
of time selected in such a manner that the measured mean particle sizes of the powder
ranged from 0.5 to 100 µm. In this manner, various samples having the compositions
as specified in Table 3 were obtained.
[0116] Comparative Examples : To obtain a crystal grain size of 100 µm or greater, the sintered
bodies were maintained for prolonged time in an argon atmosphere at a temperature
lower than the sintered temperature by 5 - 20°C.
[0117] From the thus prepared samples having the compositions as specified in Table 3 were
obtained magnets which were studied to determine their magnetic properties and their
mean crystal grain sizes. The results are set forth in Table 3. The mean crystal grain
size referred to herein was measured in the following manner:
[0118] The samples were polished and corroded on their surfaces, and photographed through
an optical microscope at a magnification ranging from x100 to x1000. Circles having
known areas were drawn on the photographs, and divided by lines into eight equal sections.
The number of grains present on the diameters were counted and averaged. However,
grains on the borders (circumferences) were counted as half grains (this method is
known as Heyn's method). Pores were omitted from calculation.
[0119] In Table 3, the samples marked
* represent comparative examples.
[0120] From the sample Nos.
*7 and
*8, it is found that He drops to less 1 kOe if the crystal grain size departs from
the scope as defined in the present invention.
[0121] Samples designated as Nos. 13 and 16 in Table 3 were studied in detail in respect
of the relationship between their mean crystal grain size D and Hc. The results are
illustrated in Fig. 10, from which it is found that He peaks when D is approximately
in a range of 3 - 10 µm, decrease steeply when D is below that range, and drops moderately
when D is above that range. Even when the composition varies within the scope as defined
in the present invention, the relationship between the mean crystal grain size D and
Hc is substantially maintained. This indicates that the Fe-Co-B-R system magnets are
the single domain particle type magnets.
[0122] From the results given in Table 3 and Fig. 10, it is evident that, in order for the
Fe-Co-B-R base magnets to possess Br of about 4 kG of hard ferrite or more and Hc
of no .less than 1 kOe, the composition comes within the range as defined in the present
invention and the mean crystal grain size D is 1 - 100 µm, and that, in order to obtain
Hc of no less than 4 kOe, the mean crystal grain size should be in a range of 1.5
- 50 µm.
[0123] Control of the crystal grain size of the sintered compact can be carried out by controlling
process conditions such as pulverization, sintering, post heat treatment, etc.

[0124] The embodiments and effects of the M-containing Fe-Co-B-R base magnets (Fe-Co-B-R-M
magnets) will now be explained with reference to the following examples given for
the purpose of illustration alone and intended not to limit the invention .
[0125] Tables 4 - 1 to 4 - 3 show properties of the permanent magnets comprising a variety
of Fe-Co-B-R-M compounds, which were prepared by melting and pulverization of alloys,
followed by forming of the resulting powders in a magnetic field then sintering. Permanent
magnets departing from the scope of the present invention are also shown with mark
*. It is noted that the preparation of samples were substantially identical with that
of the Fe-Co-B-R base magnets.
[0127] Fig. 11 shows the demagnetization curves of the typical examples of the invented
Fe-Co-B-R-M base magnets and the M-free Fe-Co-B-R base magnets. In this figure, reference
numerals 1 - 3 denote the demagnetization curves of a M-free magnet, a Mo-containing
magnet (Table 4 - 1 No. 20) and a Nb-containing magnet (Table 4 - 1 No. 16), all of
which show the loop squareness useful for permanent magnet materials.
[0128] The curve 4 represents ones with a mean crystal grain size D of 52 µm for the same
composition as 3.
[0129] In Table 5 comparative samples with marks
* are shown, wherein
*1 -
*3 are samples departing from the scope of the present invention.
[0130] From
*4 and *5, it is found that Hc drops to 1 kOe or less if the mean crystal grain size
departs from the scope of the present invention.
[0131] Samples designated as Nos. 21 and 41 in Tables 4 - 2 and 4 - 3 samples were studied
in detail in respect of the relationship between their mean crystal grain size D and
Hc. The results are illustrated in Fig. 11, from which it is found that Hc peaks when
D is approximately in a range of 3 - 10 µm, decreases steeply when D is below that
range, and drops moderately when D is above that range. Even when the composition
varies within the scope as defined in the present invention, the relationship between
the average crystal grain size D and Hc is substantially maintained. This indicates
that the Fe-Co-B-R-M base magnets are the single domain particle type magnets.
[0132] Apart from the foregoing samples, an alloy having the same composition as Sample
No. 20 of Table 4 - 1 was prepared by the (casting) procedure (1) as already stated.
However, the thus cast alloy had Hc of less than 1 kOe in spite of its mean crystal
grain size being in a range of 20 - 80 µm.
[0133] From the results given in Table 4 - 1 and Fig. 10, it is evident that, in order for
the Fe-Co-B-R-M base magnets to possess Br of about 4 kG of hard ferrite or more and
Hc of no less than 1 kOe, the composition comes within the range as defined in the
present invention and the mean crystal grain size is about 1 - about 100 µm, and that,
in order to obtain Hc of no less than 4 kOe, the mean crystal grain size should be
in a range of about 1.5 - about 50 µm.
[0134] Control of the crystal grain size of the sintered compact can be controlled as is
the case of the Fe-Co-B-R system.
[0135] As mentioned in the foregoing, the invented permanent magnets of the Fe-Co-B-R-M
base magnetically anisotropic sintered bodies may contain, in addition to Fe, Co,
B, R and M,_ impurities which are entrained therein in the process of production as
is the case for the Fe-Co-B-R system.
CRYSTAL STRUCTURE
[0136] It is believed that the magnetic materials and permanent magnets based on the Fe-Co-B-R
base alloys according to the present invention can satisfactorily exhibit their own
magnetic properties due to the fact that the major phase is formed by the substantially
tetragonal crystals of the Fe-B-R type. As already discussed, the Fe-Co-B-R type alloy
is a novel alloy in view of its Curie point. As will be discussed hereinafter, it
has further been experimentally ascertained that the presence of the substantially
tetragonal crystals of the Fe-Co-B-R type contributes to the exhibition of magnetic
properties. The Fe-Co-B-R type tetragonal system alloy is unknown in the art, and
serves to provide a vital guiding principle for the production of magnetic materials
and permanent magnets having high magnetic properties as aimed at in the present invention.
[0137] According to the present invention, the desired magnetic properties can be obtained,
if the Fe-Co-B-R crystals are of the substantially tetragonal system. In most of the
Fe-Co-B-R base compounds, the angles between the axes a, b and c are 90° within the
limits of measurement error, and ao = bo

co. Thus these compounds can be referred to as the tetragonal system crystals. The
term "substantially tetragonal" encompasses ones that have a slightly deflected angle
between a, b and c axes, e.g., within about 1°, or ones that have O
o slightly different from ℓ
o, e.g., within about 1 %.
[0138] To obtain the useful magnetic properties in the present invention, the magnetic materials
and permanent magnets of the present invention are required to contain as the major
phase an intermetallic compound of the substantially tetragonal system crystal structure.
By the term "major phase", it is intended to indicate a phase amounting to 50 vol
% or more of the crystal structure, among phases constituting the crystal structure.
[0139] The Fe-Co-B-R base permanent magnets having various compositions and prepared by
the manner as hereinbelow set forth as well as other various manners were examined
with an X-ray diffractometer, X-ray microanalyser (XMA) and optical microscopy.
EXPERIMENTAL PROCEDURES
[0140]
(1) Starting Materials (Purity is given by weight %)
Fe : electrolytic iron 99.9 %
B : ferroboron, or B having a purity of 99 %
R : 99.7 % or higher with impurities being mainly other rare earth elements
Co : electrolytic cobalt having purity of 99.9 %
(2) The experimental procedures are shown in Fig. 15.
[0141] The experimental results obtained are illustrated as below:
(1) Fig. 14 illustrates a typical X-ray diffraction pattern of the Fe-Co-B-Nd (Fe-10Co-8B-15Nd
in at %) sintered body showing high properties as measured with a powder X-ray diffractometer.
This pattern is very complicated, and can not be explained by any R-Fe, Fe-B or R-B
type compounds developed yet in the art.
(2) XMA measurement of the sintered body of (1) hereinabove under test has indicated
that it comprises three or four phases. The major phase simultaneously contains Fe,
Co, B and R, the second phase is a R-concentrated phase having a R content of 70 weight
% or higher, and the third phase is an Fe-concentrated phase having an Fe content
of 80 weight % or higher. The fourth phase is a phase of oxides.
(3) As a result of analysis of the pattern given in Fig. 14, the sharp peaks included
in this pattern may all be explained as the tetragonal crystals of αo=8.80A and co =12.23A).
[0142] In Fig. 14, indices are given at the respective X-ray peaks. The major phase simultaneously
containing Fe, Co, B and R, as confirmed in the XMA measurement, has turned out to
exhibit such a structure. This structure is characterized by its extremely large lattice
constants. No tetragonal system compounds having such large lattice constants are
found in any one of the binary system compounds such as R-Fe, Fe-B and B-R.
[0143] (4) Fe-Co-B-R base permanent magnets having various compositions and prepared by
the aforesaid manner as well as other various manners were examined with an X-ray
diffractometer, XMA and optical microscopy. As a result, the following matters have
turned out:
[0144] (i) Where a tetragonal system compound having macro unit cells occurs, which contains
as the essential components R, Fe, Co and B and has lattice constants ao of about
9 A and Go of about 12 A, good properties suitable for permanent magnets are obtained.
Table 6 shows the lattice constants of tetragonal'system compounds which constitute
the major phase of typical Fe-Co-B-R type magnets, i.e., occupy 50 vol % or" more
of the crystal structure.
[0145] In the compounds based on the conventional binary system compounds such as R-Fe,
Fe-B and B-R, it is thought that no tetragonal system compounds having such macro
unit cells as mentioned above occur. It is thus presumed that no good permanent magnet
properties are achieved by those known compounds.
[0146] (ii) Where said tetragonal system compound has a" suitable crystal grain size and,
besides, nonmagnetic phases occur which contain much R, good magnetic properties suitable
for permanent magnets are obtained.
[0147] With the permanent magnet materials, the fine particles having a high anisotropy
constant are ideally separated individually from one another by nonmagnetic phases,
since a high Hc is then obtained. To this end, the presence of 1 vol % or higher of
nonmagnetic phases contributes to the high Hc. In order that Hc is no less than 1
kOe, the nonmagnetic phases should be present in a volume ratio between 1 and 45 vol
%, preferably between 2 and 10 vol %. The presence of 45 % or higher of the nonmagnetic
phases is unpreferable. The nonmagnetic phases are mainly comprised of intermetallic
compound phases containing much of R, while oxide phases serve partly effectively.
[0148] (iii) The aforesaid Fe-Co-B-R type tetragonal system compounds occur in a wide compositional
range.
[0149] Alloys containing, in addition to the Fe-Co-B-R base components, one or more additional
elements M and/or impurities entrained in the process of production can also exhibit
good permanent magnet properties, as long as the major phases are comprised of tetragonal
system compounds.
[0150] As apparent from Table 6 the compounds added with M based on the Fe-B-R system exhibit
the tetragonal system as well as the Fe-Co-B-R-M system compounds also does the same.
Detailed disclosure regarding other additional elements M as disclosed in the European
Patent application No.83106573.5 filed on July 5, 1983 is herewith referred to and
herein incorporated.
[0151] The aforesaid fundamental tetragonal system compounds are stable and provide good
permanent magnets, even when they contain up to 1 % of H, Li, Na, K, Be, Sr, Ba, Ag,
Zn, N, F, Se, Te, Pb, or the like.
[0152] As mentioned above, the Fe-Co-B-R type tetragonal system compounds are new ones which
have been entirely unknown in the art. It is thus new fact that high properties suitable
for permanent magnets are obtained by forming the major phases with these new compounds.
[0153] In the field of R-Fe alloys, it' has been reported to prepare ribbon magnets by melt-quenching.
However, the invented magnets are different from the ribbon magnets in the following
several points. That is to say, the ribbon magnets can exhibit permanent magnet properties
in a transition stage from the amorphous or metastable crystal phase to the stable
crystal state. Reportedly, the ribbon magnets can exhibit high coercive force only
if the amorphous state still remains, or otherwise metastable Fe
3B and R
6Fe
23 are present as the major phases. The invented magnets have no sign of any alloy phase
remaining in the amorphous state, and the major phases thereof are not Fe
3B and R
6Fe
23.
[0154] The present invention will now be further explained with reference to the following
example.
EXAMPLE
[0155] An alloy of 10 at % Co, 8 at % B, 15 at % Nd and the balance Fe was pulverized to
prepare powders having an average particle size of 1.1 µm. The powders were compacted
under a pressure of 2 t/cm
2 and in a magnetic field of 12 kOe, and the resultant compact was sintered at 1080°C
for 1 hour in argon of 1.5 Torr.
[0156] X-ray diffraction has indicated that the major phase of the sintered body is a tetragonal
system compound with lattice constants Qo=8.79A and co=12.21A. As a consequence of
XMA and optical microscopy, it has been found that the major phase contains simultaneously
Fe, Co, B and Pr, which amount to 90 volume % thereof. Nonmagnetic compound phases
having a R content of no less than 80 % assumed 4.5 % in the overall with the remainder
being substantially oxides and pores. The mean crystal grain size was 3.1 µm.
[0157] The magnetic properties measured are : Br = 12.0 kG, iHc = 9.2 kOe, and (BH)max =
34MGOe, and are by. far higher than those of the conventional amorphous ribbon magnet.
[0158] By measurement, the typical sample of the present invention has also been found to
have high mechanical strengths such as bending strength of 25 kg/mm
2, compression strength of 75 kg/mm
2 and tensile strength of 8 kg/mm
2. This sample could effectively be machined, since chipping hardly took place in machining
testing.
[0159] As is understood from the foregoing, the present invention makes it possible to prepare
magnetic materials and sintered anisotropic permanent magnets having high remanence,
high coercive force and high energy product with the use of less expensive alloys
containing light-rare earth elements, a relatively small amount of Co and based on
Fe, and thus present a technical breakthrough.
1. A magnetic material comprising Fe, B, R wherein R is at least one rare earth element
including Y, and Co, and in which a major phase is formed of at least one intermetallic
compound of the Fe-Co-B-R type having a crystal structure of the substantially tetragonal
system.
2. A sintered magnetic material having a major phase formed of at least one intermetallic
compound consisting essentially of, by atomic percent , 8 - 30 percent R wherein R
is at least one of rare earth elements including Y, 2 - 28 percent B, more than zero
and not exceeding 50 percent Co, and the balance being Fe with impurities.
3. A sintered magnetic material having a major phase formed of at least one intermetallic
compound of the substantially tetragonal system, and consisting essentially of, by
atomic percent, 8 - 30 percent R wherein R is at least one rare earth element including
Y, 2 - 28 percent B, more than zero and not exceeding 50 percent Co, and the balance
being Fe with impurities.
4. A sintered anisotropic permanent magnet consisting essentially of, by atomic percent,
8 - 30 percent R wherein R is at least one rare earth element including Y, 2 - 28
percent B, more than zero and not exceeding 50 percent Co, and the balance being Fe
with impurities.
5. A sintered anisotropic permanent magnet having a major phase formed of at least
one intermetallic compound of the Fe-Co-B-R type having a crystal structure of the
substantially tetragonal system, and consisting essentially of, by atomic percent
8 - 30 percent R wherein R is at least one rare earth element including Y, 2 - 28
percent B, more than zero and not exceeding 50 percent Co, and the balance being Fe
with impurities.
6. A magnetic material as defined in Claim 1 or 3, in which the substantially tetragonal
system amounts to no less than 50 vol %.
7. A permanent magnet as defined in Claim 5, in which the substantially tetragonal
system amounts to no less than 50 vol %.
8. A permanent magnet as defined in Claim 7, which contains no less than 1 vol % of
nonmagnetic intermetallic compound phases.
9. A permanent magnet as defined in Claim 4 or 5, in which the mean crystal grain
size is 1 to 100 µm.
10. A permanent magnet as defined in Claim 9, in which the mean crystal grain size
is 1.5 to 50 µm.
11. A permanent magnet as defined in Claim 4 or 5, in which R is 12 - 24 %, and B
is 3 - 27 %.
12. A permanent magnet as defined in Claim 11, in which R is 12 - 20 %, and B is 4
- 24 %.
13. A permanent magnet as defined in Claim 12, in which Co is 5 - 45 %.
14. A permanent magnet as defined in Claim 4 or 5, in which Co is no more than 25
%.
15. A permanent magnet as defined in Claim 4 or 5, in which Co is 5 % or more.
16. A permanent magnet as defined in Claim 4 or 5, in which the light-rare earth element(s)
amounts to no less than 50 at % of the overall rare earth elements R.
17. A permanent magnet as defined in Claim 16, in which the sum of Nd plus Pr amounts
to no less than 50 at % of the overall rare earth elements R.
18. A permanent magnet as defined in Claim 16 or 17, in which R is about 15 %, and
B is about 8 %.
19. A permanent magnet as defined in Claim 4 or 5, in which the maximum energy product
(BH)max is no less than 4 MGOe.
20. A permanent magnet as defined in Claim 11, in which the maximum energy product
(BH)max is no less than 7 MGOe.
21: A permanent magnet as defined in Claim 12, in which the maximum energy product
(BH)max is no less than 10 MGOe.
22. A permanent magnet as defined in Claim 21, in which the maximum energy product
(BH)max is no less than 20 MGOe.
23. A permanent magnet as defined in Claim 22, in which the maximum energy product
(BH)max is no less than 30 MGOe.
24. A permanent magnet as defined in Claim 23, in which the maximum energy product
(BH)max is no less than 33 MGOe.
25. A magnetic material which comprises Fe, B, R wherein R is at least one rare earth
element including Y, Co, and at least one element M selected from the group given
below in the amounts of no more than the values specified below, wherein when more
than one element comprises M, the sum of M is no more than the maximum value among
the values specified below of said elements M actually added and the amount of M is
more than zero, and in which a major phase is formed of at least one intermetallic
compound of the Fe-Co-B-R type having a crystal structure of the substantially tetragonal
system:
26. A sintered magnetic material having a major phase formed of at least one intermetallic
compound consisting essentially of, by atomic percent, 8 - 30 percent R wherein R
is at least one rare earth element including Y, 2 - 28 percent B, no more than zero
and not exceeding 50 percent Co, at least one additional element M selected from the
group given below in the amounts of no more than the values specified below wherein
when more than one element comprises M, the sum of M is no more than the maximum value
among the values specified below of said elements M actually added and the amount
of M is more than zero, and the balance being Fe with impurities:
27. A sintered magnetic material having a major phase formed of at least one intermetallic
compound of the substantially tetragonal system, and consisting essentially of, by
atomic percent, 8 - 30 percent R wherein R is at least one rare earth element including
Y, 2 - 28 percent B, more than zero and not exceeding 50 percent Co, at least one
additional element M selected from the group given below in the amounts of no more
than the values specified below wherein when more than one element comprises M, the
sum of M is no more than the maximum value among the values specified below - of said
elements M actually added and the amount of M is more than zero, and the balance being
Fe with impurities:
28. A sintered anisotropic permanent magnet consisting essentially of, by atomic percent,
8 - 30 percent R, wherein R is at least one rare earth element including Y, 2 - 28
percent B, more than zero and not exceeding 50 percent Co, at least one additional
element M selected from the group given below in the amounts of no more than the values
specified below, wherein the amount of M is not zero and wherein when more than one
element comprises M, the sum of M is no more than the. maximum value among the values
specified below of said elements M actually added, and the balance being Fe with impurities:
29. A sintered anisotropic permanent magnet having a major phase formed, of at least
one intermetallic compound of the Fe-Co-B-R type having a crystal structure of the
substantially tetragonal system and consisting essentially of, by atomic percent,
8 - 30 percent R wherein R is at least one rare earth element including Y, 2 - 28
percent B, more than zero and not exceeding 50 percent Co, at least one additional
element M selected from the group given below in the amounts no more than the values
specified below, wherein the amount of M is not zero and wherein when more than one
element comprises M, the sum of M is no more than the maximum value among the values
specified below of said elements M actually added, and the balance being Fe with impurities:
30. A magnetic material as defined in Claim 25 or 27, in which the substantially tetragonal
system amounts to no less than 50 vol %.
31. A permanent magnet as defined in Claim 29, in which the substantially tetragonal
system amounts to no less than 50. vol %.
32. A permanent magnet as defined in Claim 31, which contains no less than 1 vol %
of nonmagnetic intermetallic compound phases.
33. A permanent magnet as defined in Claim 28 or 29, in which the mean crystal grain
size is 1 to 100 µm.
34. A permanent magnet as defined in Claim 33, in which the mean crystal grain size
is 1.5 to 50 µm.
35. A permanent magnet as defined in Claim 28 or 29, in which R is 12 to 24 %, and
B is 3 to 27 %.
36. A permanent magnet as defined in Claim 35, in which R is 12 to 20 %, and B is
4 to 24 %.
37. A permanent magnet as defined in Claim 36, in which Co is 5 - 45 %.
38. A permanent magnet as defined in Claim 28 or 29, in which Co is no more than 25
%.
39. A permanent magnet as defined in Claim 28 or 29, in which Co is 5 % or more.
40. A permanent magnet as defined in Claim 31 or 32, in which the light rare earth
element(s) amounts to no less than 50 at % of the overall rare earth elements R.
41. A permanent magnet as defined in Claim 40, in which the sum of Nd plus Pr amounts
to no less than 50 at % of the overall rare earth elements R.
42. A permanent magnet as defined in Claim 40 or 41, in which R is about 15 %, and
B is about 8 %.
43. A permanent magnet as defined in Claim 28 or 29, in which the maximum energy product
(BH)max is no less than 4 MGOe.
44. A permanent magnet as defined in Claim 35, in which the maximum energy product
(BH)max is no less than 7 MGOe.
45. A permanent magnet as defined in Claim 36, in which the maximum energy product
(BH)max is no less than 10 MGOe.
46. A permanent magnet as defined in Claim 45, in which the maximum energy product
(BH)max is no less than 20 MGOe.
47. A permanent magnet as defined in Claim 46, in which the maximum energy product
(BH)max is no less than 30 MGOe.
48. A permanent magnet as defined in Claim 47, in which the maximum energy product
(BH)max is no less than 33 MGOe.